Shabab, the Al Qaeda-affiliated Somali militant group claiming responsibility for a deadly assault Saturday on an upscale Nairobi shopping mall, has been implicated in a string of attacks in Kenya in recent years.
The group has been issuing threats against Kenya since the country sent troops into southern Somalia in 2011 and helped drive the militants out of the port city of Kismayo, once a key source of Shabab's revenue, the following year. Kenya still has troops in Somalia operating under the banner of the African Union.
In a series of Twitter messages Saturday, the Shabab media office said the attack on the Westgate shopping mall was "retributive justice" for Kenya's actions in Somalia.
"For long we have waged war against the Kenyans in our land, now it's time to shift the battleground and take the war to their land," the group said in one tweet.
Shabab, which means "youth" in Arabic, has waged a long-running rebellion against Somalia's weak government.
The group was pushed from the Somali capital, Mogadishu, in 2011 by a U.S.- backed force from African Union countries. Last year, Somalia installed its first elected government since the country collapsed into civil war in 1991, followed by more than two decades of bloodshed, hunger and lawlessness.
But Shabab continues to control many rural areas, where it enforces a strict interpretation of sharia, or Islamic law.
The militants have claimed responsibility for high-profile attacks in Somalia and beyond its borders, including twin bombings in the Uganda capital, Kampala, that killed 76 people who had gathered to watch the July 2010 World Cup soccer championship game at a restaurant and rugby club.
Shabab's attacks in Kenya have included bombings, shootings and grenade attacks, although none on the scale of Saturday's assault. The Westgate mall, which houses Western stores and is popular with wealthy Kenyans and expatriates, was an obvious target.